1. Field of the Invention
This invention relates generally to temperature sensitive films and more specifically to the use of such a film to aid in locating the veins in the arm, hand or any prefixed area of a patient prior to taking a blood sample or the infusion of fluid into the patient by invasive techniques. The invention relates generally to the temperature sensitive film and specifically to the method of using the film.
2. Description of the Prior Art
One of the most common medical tests or procedures performed on patients is associated with the analysis of the blood of the patient or the infusion of fluid into the patient by invasive techniques. Usually the first step in such a test procedure involves the taking of a sample of the patient's blood or the infusion of fluid into the patient by invasive techniques. Typically by puncturing a vein in the arm of the patient using a needle and syringe or a needle set. Of course, in order to puncture the vein of the patient, the vein must first be located in the arm.
The location of the vein is not particularly difficult if it can be visually sighted or felt. In order to enhance the probability of visual sighting or feeling, an elastic strap is usually tightly wound around the upper arm of the patient. This produces a differential in the pressure of the blood being conducted by the veins. The human body responds to such a pressure differential by enlarging the veins in an attempt to provide a conduction path of less resistance. The enlarging of the veins makes them more prominent and therefore increases the probability that one of the veins can be located by viewing or feeling the arm of the patient.
Even when this procedure for enlarging the veins has been followed, there have been many cases where the veins could neither be sighted nor felt. Many factors are responsible for this result. Since the vein is generally dark in color, it is even more difficult to sight a vein in the arm of a person having a dark colored pigment in his skin. Other characteristics of the patient which make it particularly difficult to sight or feel a vein are associated with small children, obesity, and old age. These characteristics generally mean that the vein is significantly recessed from the skin and therefore particularly difficult to visually sight or feel.
In those cases where the vein can neither be sighted nor felt, a blood sample is typically taken only after repeatedly puncturing the arm of the patient or probing within the arm of the patient in an attempt to locate the vein. This of course is painful to the patient during the probing process and often leaves the patient with a substantial bruise after the blood sample is taken.
Liquid crystal materials are generally well known to provide a colorplay temperature range within which the material will provide color variations in response to different temperatures of the material in the colorplay range. The liquid crystal material has been enclosed in capsules which in turn have been drawn down on a plastic backing in a vacuum chamber to provide a particular layer of the encapsulated liquid crystal material. A black ink has been used to cover the particular layer to facilitate the detection of the color differences of the liquid crystal material. Such a device appears to have been disclosed in an Information and Instructions notice Number 711317-1 (Rev. 11-69) prepared by Edmund Scientific Co., Barrington, New Jersey. The process of drawing the encapsulated liquid crystal material onto the backing in a vaccum chamber has provided significant variations, in the thickness of the particular layer. For example, the thickness has varied as much as 50 percent of the maximum thickness of the layer over approximately 90 percent of the layer. These variations in the thickness of the layer have left the layer with voids and also reduced the sensitivity of the temperature sensitive film to slight variations in temperature. Furthermore, the thickness of the different layers have been so thick that a low sensitivity of the resultant article has resulted when the articles have been placed upon a patient's skin. This has prevented such articles from indicating the location of veins on a patient.